1. Field
This invention relates to snowmobile skis and in particular to snowmobile skis which are versatile, being useful on ice, hard-packed snow or in deep, powdery snow.
2. State of the Art
Snowmobile skis have undergone considerable evolution in recent years. Traditionally, metal skis had been utilized for decades until the recent development of plastic skis. Also, skis have gone from being essentially flat to having a curved or rocker shape as illustrated and claimed in various U.S. patents to Noble, namely, U.S. Pat. No. 5,700,020; U.S. Pat. Nos. 6,012,728 and 6,267,392. The later two patents also introduced the concept of having a plurality of keels and especially a tri-keel design wherein there is a central longitudinal keel which is deeper than two outboard keels. The advantage of this triple keel design is that it permits the skis to be more versatile, giving traditional steering control on hard surfaces, for example, ice, via the central keel, and then in deeper snow where the outboard keels take over some of the function of the central keel in permitting easy, straight-ahead steering and providing better control in turns, especially in deeper snow.
U.S. Pat. No. 4,491,333 to Warnke discloses a flat ski with flared flat running surface extensions to maximize ski flotation in deep snow. These flat wings are an extension of the ski running surface in that the margins of the ski are flared upward at an angle of 30° to 60° to the snow surface. The patent states that better lift is achieved in turns in deep snow without affecting the characteristics of the skis when run on hard pack snow. The flared ski margins serve to increase the effective width of the skis.
Snowmobiles have a long extended track which tends to cause the snowmobile to proceed along the longitudinal axis of the track even in a turn. The long track is rapidly moving and it tends to propel the snowmobile straight ahead even when the skis are turned, thus there is a plowing action of the skis in turns. Skis having some vertical surface area such as provided by the three keels militate to some extent against the sideways or lateral motion of turned skis. The snowmobile steering mechanism is structured with a camber so that when the snowmobile skis are turned the skis tilt away from a flat, running aspect. The straight-ahead, plowing effect may be pronounced in deep snow at any speed where the snow is very powdery and light such as that found frequently in the western United States.